Actually, I don't see the match-up problem ... with the Mavs anyway.
Parker - Manu - Bowen as about the same as Parker - Wells - Bowen. Either way Howard gets to play defense on a SG, as Bowen is hardly worth guarding (until he steps into the corner)
The real problem would be Parker - Manu - Wells. That would be a problem with other teams but then the Mavs just come with Buckner and Howard to guard the Manu and Wells.
I don't really see the match-up problem.
The Spurs are not giving up much for such a player. Williams is about done, Barry is done and Scola .... He has yet to play at this level, it's like Oberto, you never know till they actualy play the game at this level. Its in a teams best interest to "talk up" the talent that they have or have aquired, both for their fans and for other teams that don't do the same level of homework before trades. I will believe Scola is "very good" when I see him play at this level.
I think I would look for a better deal then William, Barry and Scola for a player like Wells.